The present invention is in the technical field of acid detection. More particularly, the present invention is in the technical field of acid detection in vapor compression heating, air conditioning, and refrigeration systems, and is an electronic acid detector and method that uses infrared absorbance to determine the type and concentration of acid in a system as well as to detect moisture.
Vapor compression refrigerators, heat pumps, and air conditioners must always be concerned with the presence of acids in the refrigerant which can severely shorten the life of both the compressor and refrigerant. These acids can be formed by chemical reactions of the refrigerant or refrigeration oil with moisture, components and/or materials of construction, and/or impurities. The instabilities of the refrigerants and refrigeration oils are accelerated by elevated temperatures which result from improper operation, such as a failed condenser fan, or clogged air flow path.
Checking the refrigerant and/or oil acid is a common maintenance procedure because acidic compounds can be cleaned up before permanent damage to the hardware and refrigerant occur. Acids in a refrigeration system can potentially result in hermetic compressor motor burn-out because the acid will degrade the motor winding's electrical insulation, causing an electrical short. Acids in a refrigeration system can also form high-viscosity sludge which does not provide adequate lubrication and can also clog the expansion device. The presence of acid indicates the existence of other decomposition products, such as non-condensable gases, which result in elevated pressures leading to reduced efficiency and overloaded compressor operation.
To avoid the above-mentioned problems, refrigeration systems are tested for acid content. Typically, the oil would be tested for acid, because the highest concentration of acid is found in the oil of a non-operating system (shut down). It is, however, much easier to test the system for acid while operational. Several indicator systems are known for testing the presence and concentration of contaminants in a refrigerant. For example, U.S. Pat. Nos. 4,923,806 and 5,071,768 show apparatuses for testing liquid or vapor contaminants in a closed system whether the apparatus is operating or not. A disposable testing tube made of transparent material is used at the end of a compressor discharge line or elsewhere in the system. One section of the tube is provided with water removal and moisture indicating chemicals, such as cobaltus chloride and another section is provided with acid indicating chemicals such as a solution of bromophenol blue, ethanol, and glycerol. This construction is relatively complicated and requires a separate, specially configured flow restrictor in addition to a tube holder, and an expensive testing tube in which the multiple contaminant testing chemicals and filter screens are located.
Likewise, U.S. Pat. No. 5,377,496 shows an acid contamination indicator for closed loop vapor compression systems in which the indicator is permanently or removably installed in the bypass line around the system compressor where the refrigerant is always in the gaseous phase. A casing has a visual indicator bed of bromophenol blue as the acid indicating medium which is contacted by the refrigerant after flowing through a filter and a flow restrictor orifice. Porous retainer discs are held against the bed by springs. The solid indicator must be mixed with an inert substance to provide some porosity, contact surface area, and increased volume and then packaged in a clear tube. Again, we have recognized that this is an unduly complicated construction which requires a substantial outlay for installation.
Another type of contaminant detector is marketed by Refrigeration Technologies of Fullerton, Calif. under the trademark “CHECKMATE”. A specific volume of gas passes through a detection tube at a predetermined termination pressure. However, an expensive sealed Pyrex detection tube containing a color-changing chemical and whose ends are pierced when fully assembled can only be used once even when the test is negative, and thus this approach entails considerable expense regardless of its technical merits. These systems were also developed to detect inorganic mineral acids, which are highly corrosive and therefore easier to detect. With the new refrigerants and oils, mild organic acids are typically formed. These acids which can lead to slug formation, are more difficult to detect.
Electronic refrigerant leak detectors operate on a variety of principles including heated diodes as in U.S. Pat. No. 3,739,260, negative corona discharge as in U.S. Pat. No. 4,488,118, and infrared (IR) absorbance as in U.S. Pat. No. 6,791,088. The method disclosed in the latter patent can be summarized thusly: After the IR signal is detected electrically, it is filtered through a band pass filter and then amplified. The signal is then sent through an accumulator/peak detector with a large capacitor to store small signals for a longer period of time; it then is passed into a subtracting op-amp to remove any zero offset set by the potentiometer. The signal is then further processed and delivered to the user as feedback via a lighted display indicating leak intensity. However, no prior art instrument has recognized or addressed the detection of acids as well as moisture in an HVAC/R system using IR detection methods.
Infrared absorbance has been used to monitor the presence of a large variety of gases, including acids. This technology is described in U.S. Pat. No. 7,253,413 and has been commercialized by Smiths Detection Inc. as the “GasID” portable gas and vapor chemical identifier. This device is used for the identification of flammables, corrosives, toxic industrial chemicals, and weapons of mass destruction. The system uses a pump to deliver the gaseous sample to an adsorbent bed where the sample can be concentrated for full-spectrum IR analysis. An attached computer then processes the spectral data and a graphical user interface conveys information such as chemical identification to the operator. The gas is sampled for approximately 10 minutes before matches are communicated to the operator. This apparatus is too complicated, expensive, and slow to be used as a portable hand-held device for the portable detection of acids in an HVAC/R system located in the field.